1. Technical Field
The present invention relates to a radio transmission apparatus.
2. Related Art
Since service providers can use specified low-power radio used for telemeter, telecontrol, data transmission, or the like without receiving license of radio stations in conformity to radio laws, the specified low-power radio has recently been used widely in various communication devices. In ARIB STD-T67 which is a standard of the specified low-power radio, multiple channels are defined at intervals of 12.5 kHz or intervals of 25 kHz in the 400 MHz bandwidth. Thus, in radio transmission apparatuses conforming to ARIB STD-T67, precision of a transmission frequency is requested to be within ±4 ppm in a full temperature range to be used in each channel to be used. In the related art, a radio transmission apparatus in which the request for such frequency precision is difficult includes a temperature compensated crystal oscillator (TCXO), a radio transmission integrated circuit (IC), and a controller, as illustrated in FIG. 11. The request for frequency precision has been satisfied by performing frequency conversion on an output signal of the temperature compensated crystal oscillator (TCXO) by the radio transmission IC under the control of the controller and generating a carrier wave of a desired frequency. Such a radio transmission apparatus is disclosed in, for example, JP-A-2008-85899.
However, since the temperature compensated crystal oscillator (TCXO) is an expensive component, there is a problem that a radio transmission apparatus of the related art including a temperature compensated crystal oscillator (TCXO) is necessarily expensive. In particular, since low cost is necessary in a miniature radio device such as a restaurant order-bell, it is difficult to use an expensive component such as a temperature compensated crystal oscillator (TCXO) included in a radio transmission apparatus.